Abstract
Variability in the nature, over a small area, of soils derived from coarse-grained rocks have been widely reported. Such reports concerning soils from fine-grained rocks are however sparse. Some geotechnical properties of a laterite soil derived from a fine-grained amphibolite have been investigated with a view to ascertain its variability.
Samples of the soil were taken from the same horizon within an area of about one square metre. The basis index properties, chemistry, mineralogy and microstructure of the sol samples have been investigated.
Despite the similarities in the grain-size distribution. Atterberg limits and chemistry of the samples, large variations were obtained in the mineralogy as evidenced by the goethite content, as well as in the micro-structure.
The variation in the microstructure is attributed to the inconsistent cementation of the soil particles by non-uniformly distributed goethite which itself is believed to be a result of the variations in the Eh-pH conditions within the soil. The implications of this microstructural variation on the geotechnical properties of the undisturbed soil is assessed.
Résumé
Il existe de nombreux comptes rendus sur les variations de composition dans un même secteur limté de sols issus de roches à gros grain. Par contre les données concernant les sols issus de roches à grain fin sont assez rares. Le présent article étudie les caractéristiques géotechniques d'un sol latéritique issu d'une amphibolite à grain fin.
Les échantillons de sol ont été prélevés dans le même horizon et sur une surface d'environ un mètre carré. Les propriétés classiques (granularité. limites “d'Atterberg) les caractéristiques chimiques” et minéralogiques ainsi que la microstructure ont été étudiées.
En dépit de granularités, de valeurs de limites d'Atterberg et de propriétés chimiques voisines, on constate des variations importantes des caractéristiques chimiques (teneur en goethite en particulier) et de la microstructure.
Les différences de microstructure sont attribuées à la répartition non uniforme de la cimentation des particulales de sol par la goethite, dont la teneur dépend apparemment des variations des conditions de Eh-pH à l'intérieur du sol. Les conséquences de ces variations de micro-structure sur les propriétés géotechniques du sol intact sont exposées.
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Ogunsanwo, O. Basic index properties, mineralogy and microstructure of an amphibolite derived laterite soil. Bulletin of the International Association of Engineering Geology 33, 19–25 (1986). https://doi.org/10.1007/BF02594701
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DOI: https://doi.org/10.1007/BF02594701